Dry ice sticks to restore flow in wells



United States Patent 3,316,968 DRY ICE STICKS T0 RESTORE FLOW IN WELLS Henry D. Nettles, Tyler, Tex., assignor to Pan American Petroleum Corporation, Tulsa, Okla., a corporation of Delaware No Drawing. Filed Mar. 25, 1964, Ser. No. 354,752 7 Claims. (Cl. 166-45) ABSTRACT OF THE DISCLOSURE Flow of oil or gas from wells is restored by dropping solid carbon dioxide sticks down the well tubing. Carbon dioxide gas is thus generated to lift at least part of the liquid from the tubing so the bottom hole pressure is again able to cause flow of fluids up the tubing.

In many oil wells the pressure at the bottom of the well is suflicient to force the oil to flow to the surface of the earth through a string of tubing in the well. Eventually, the pressure drops to a point where the oil must be pumped from the well. Between the conditions under which a Well has more than enough pressure to cause flow to the surface and the time when the well must be pumped is a range of conditions where the well may or may not flow, depending upon the liquids in the tubing. For example, if a Well has been shut in for a period of time due to proration laws or other reasons, the oil in the tubing may become dead. That is, the oil may lose its normal gas content. This is particularly true if a slight leak of gas occurs from the tubing at the well head. Loss of the gas from the oil increases the density of the oil. In addition, leakage of gas allows the oil level to rise in the tubing. When the top of the tubing is again opened, the well may not flow. The hydraulic head of the dead oil may equal the pressure at the bottom of the well. It is also possible that the tubing may become partly filled with brine having a higher density than the oil. Once the well is made to flow, however, the dead oil or the brine is quickly replaced in the tubing by live oil containing gas. Due to the lower density of this gas-containing oil, the well may continue to flow when once kicked off.

A common way of kicking off a well is to run a swab down the tubing on a wire line and withdraw the swab with a load of dead oil on top. Removal of the load of dead oil usually initiates flow of the well. This operation of running a swab in a well requires bringing special equipment to the well and is usually rather expensive.

An object of my invention is to provide a method for initiating flow from a well which will continue to flow once flow is started. A more specific object of the invention is to provide a method which does not require specialized equipment for initiating flow from a well. Still other objects will be apparent to those skilled in the art from the following description and claims.

In general I accomplish the objects of my invention by dropping solid carbon dioxide, sometimes known as Dry Ice, down a well.

This method has been applied to wells in the East Texas Field. These wells flow with a normal surface pressure of about 35 to 200 pounds per square inch gage and a relatively low gas-oil ratio. Very small amounts of water production frequently build up in the well bore and create sufficient backpressure to cause wells to cease flowing. Even a small leak in surface controls on these wells may permit bleed-off of gas energy which will cause these wells to cease flowing.

The method of using Dry Ice has been, and is still being, applied to dead flowing wells in this field. The method causes the wells to resume flowing successfully.

3,316,536! Patented May 2, 1961 Cakes of Dry Ice are sawed into sticks approximatel 1 inch square in cross section by 12 inches long. Thl sticks are then dropped into the tubing string at the sur face and the well is left shut in for one to two hours unti the Dry Ice has had time to sublimate due to well fluir heat and change into gaseous carbon dioxide. When tht well is opened to flow, the expansion of the carbon di oxide lightens the oil column holding backpressure or the formation and the oil flow is resumed. No additive other than the Dry Ice is used in the East Texas wells.

This method has been applied to 25 East Texas Well: with success in restoring flow on 22 wells. The failures that occurred on the other three .wells were due to casing leaks or breakthrough of formation water which provided such volumes of water that normal reservoir pressure was insuflicient to permit flowing production.

The normal method which has beenused to restore East Texas wells to flowing condition is to swab them at a cost of approximately per well. The average amount of Dry Ice sticks placed in wells has been about 6 pounds per well at a cost of approximately 50 cents.

Frequently, it is not necessary that this process be repeated each time a well is shut in. A number of East Texas wells have continued to flow satisfactorily with only one treatment. In general, wells with high surface pressures and high gas-oil ratios will require few treatments. Wells with low surface pressures and low gas-oil ratios, on the other hand, may require treatment each time after being shut in. At the low cost indicated above, it will be apparent that dead wells can continue to be kicked off by my method long after the use of other more expensive methods must be abandoned.

Many variations are possible on the treatment used in the East Texas wells. For example, in some cases only a pound or two of Dry Ice will be required and the shut in time may be substantially zero. This is in case the oil level in the tubing is only a few feet below the surface flow line so that a very small amount of gas near the surface of the oil will lift some of the oil over into the flow line thus decreasing the hydrostatic head and initiating flow. In other cases, a large amount of Dry Ice on the order of 10 to 20 pounds or even more may be used to saturate a long column of oil with carbon dioxide. The shut in time may be extended beyond two hours in order to allow the Dry Ice to fall to a lower depth in the well and saturate a longer column of oil, and perhaps brine, with carbon dioxide.

The size and shape of the Dry Ice particles may vary within wide limits. Preferably, however, the Dry Ice should be dropped down the tubing in chunks of as large a cross section as possible so they will sink to a greater depth in the tubing before they completely sublime into the gaseous state. The chunks may be of any shape and may be dropped at any rate. Spherical chunks, or sticks with a length exceeding the tubing diameter by a factor of at least 3 or 4, are preferred. More angular pieces of Dry Ice, such as cubes, if dropped in quick sequence, may wedge and bridge in tubing joints at a shallow level. Fortunately, it is only necessary to wait a short time for the bridge to sublime and thus be removed. In order to avoid excessively rapid sublimation, the minimum dimension of the chunk of Dry Ice should be at least about /2 inch and preferably at least about 1 inch.

While the method has been described principally in connection with oil wells, it will be apparent that the method is also applicable to certain other wells. For example, many gas wells also produce some water. In some cases the water builds up in the tubing of a gas well until the hydraulic head of the water balances the bottom hole gas pressure. In such cases, chunks of Dry Ice can be used to gas lift part of the water out of the Well so the remaining water can be blown out by flowing natural gas.

Still other variations and modifications of my process ll be apparent to those skilled in the art. For example, aming agents m-ay be introduced with, or incorporated 10, the Dry Ice sticks to improve the tendency of the rbon dioxide to lift the oil and brine from the well. 1e examples and descriptions given above are by way of ample only. Therefore, I do not wish to be bound by ese examples, but only by the following claims.

I claim:

1. A method for initiating flow of liquid from a well tmprising dropping solid carbon dioxide into said liquid the condu-it through which said liquid flows to the surce and producing said liquid together with gaseous cardioxide from said well, no gas-generating additive :her than the solid carbon dioxide being used in the e11.

2. The method of claim 1 in which said liquid is crude :troleum.

3. The method of claim 1 in which said well is a gas ell and said liquid is water.

4. The method of claim 1 in which the amount of solid arbon dioxide is from about 2 to about 20 pounds.

5. The method of claim 1 in which said solid carbon ioxide is introduced in chunks having a minimum di- Jension of at least about /2 inch.

6. The method of claim 1 in which said well is shut in for at least about an hour immediately after said solid carbon dioxide is introduced, before said liquid and said gaseous carbon dioxide are produced from said well.

7. The method of claim 1 in which said solid carbon dioxide is introduced in the form of sticks having a minimum dimension of at least about 1 inch and a length of about 12 inches.

References Cited by the Examiner UNITED STATES PATENTS 2,623,596 12/ 1952 Whorton 166-7 2,811,209 10/ 1957 Elkins 166-43 X 3,076,508 2/1963 Lissant 166-45 3,100,528 8/1963 Plummer 166-42 3,170,517 2/ 196-5 Graham 166-42 3,227,210 1/ 1966 Trantham 166-9 FOREIGN PATENTS 1,223,078 1/1960' France.

CHARLES E. OCONNELL, Primary Examiner.

N. C. BYERS, Assistant Examiner. 

1. A METHOD OF INITIATING FLOW OF LIQUID FROM A WELL COMPRISING DROPPING SOLID CARBON DIOXIDE INTO SAID LIQUID INT HE CONDUIT THROUGH WHICH SAID LIQUID FLOWS TO THE SURFACE AND PRODUCING SAID LIQUID TOGETHER WITH GASEOUS CARBON DIOXIDE FROM SAID WELL, NO GAS-GENERATING ADDITIVE OTHER THAN THE SOLID CARBON DIOXIDE BEING USED IN THE WELL. 